1. Field of the Invention
This invention relates to CDMA systems, and more specifically to handover area detection in CDMA systems.
2. Description of the Related Art
In Code Division Multiple Access (CDMA) systems, a soft handover (SHO) area is characterized by similarly strong pilot power signals (CPICH Ec/Io in Wideband CDMA (WCDMA)). Pilot powers are measured by the mobile in idle as well as in connected mode. In connected mode, it is very important that the mobile is always connected to the strongest cell(s). Otherwise, it would cause significant interference in uplink and waste network capacity. In idle mode, it is important to camp in the strongest cell to allow a quick call initiation and not cause interference at call initiation.
A new situation arises if the mobile has to detect a soft handover (SHO) area in another band than the currently serving. When new downlink (DL) carriers are allocated for FDD-WCDMA (Frequency Division Duplex-Wideband CDMA) it is possible to be connected in a DL2 carrier (e.g., extension band carrier) and cause uplink (UL) interference without being able to detect the interference situation in the DL2 carrier. The current 3GPP procedures don't foresee the SHO area detection in another band to avoid UL interference. Connected mode inter-frequency measurements in compressed mode are event triggered and for handover purposes.
If two or more DL bands are associated to one UL band, a SHO area in DL1/UL band might not be a SHO area in the DL2 band. Effectively, if the mobile is camping or in connected mode in the DL2 band, it cannot notice when it enters the SHO area in the DL2/UL band. But UL being the same for both DL bands the mobile then will cause significant UL interference when starting transmission.